The present invention relates to methods of manufacturing semiconductor devices and, more particularly, to a method of manufacturing a pressure microsensor on a silicon substrate.
Two techniques are known for producing pressure, acceleration and similar microsensors which include the formation of thin diaphragms on a substrate of semiconductor material. One of these techniques is based on the machining of a wafer of semiconductor material on both of its faces, essentially by means of anisotropic chemical attack (bulk micromachining). The other is based on machining on a single face of a wafer of semiconductor material by the deposition of thin layers and the selective removal of a portion of an inner or buried layer with the use of isotropic chemical attack (surface micromachining). The latter technique is particularly suitable for the integration of the sensor with processing circuits associated therewith.
A method of manufacturing microstructures by the xe2x80x9csurface micromachiningxe2x80x9d technique is the subject of European patent application No. 96830437.8 filed by the Applicant on Jul. 31, 1996, hereby incorporated by reference, and is described briefly below with reference to FIGS. 1-4. This method provides for the formation of a silicon dioxide region 10 on a monocrystalline silicon substrate 11 (FIG. 1), the formation by epitaxial growth of a silicon layer in which polycrystalline silicon 12 grows on the silicon dioxide region 10 and monocrystalline silicon 13 grows on the rest of the substrate (FIG. 2), the formation of holes 14 in the polycrystalline portion of the silicon layer (FIG. 3), and the removal of the silicon dioxide region 10 by chemical attack with hydrofluoric acid through the holes 14 (FIG. 4) so as to form a space 15 beneath a diaphragm of polycrystalline silicon 12xe2x80x2.
The object of the present invention is to produce an absolute pressure sensor with the use of the xe2x80x9csurface micromachiningxe2x80x9d technique. This requires the formation of a structure similar to that obtainable by the known method described above, but in which the space defined by the polycrystalline silicon diaphragm is closed hermetically.
Accordingly, the present invention provides a method of manufacturing a pressure microsensor on a silicon substrate. The method comprises the steps of forming a region of a selectively removable material on the substrate, forming a silicon layer on this region and on the substrate, forming holes in the silicon layer above the region, removing the material from the region by selective chemical attack through the holes until a diaphragm of predetermined thickness constituted substantially by a portion of the aforesaid silicon layer, attached to the substrate along the edges and separated therefrom by a space, is produced, and forming means for detecting mechanical deformation of the diaphragm. The holes have widths smaller than the thickness of the diaphragm, and after the diaphragm has been produced, a layer of silicon dioxide which closes the holes is formed by vapor-phase deposition at atmospheric pressure on the portion of the silicon layer which constitutes the diaphragm.
Additional objects, advantages, novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.